<html>
<head>
	<meta charset="UTF-8">
	<meta content="IE=edge" http-equiv="X-UA-Compatible">
	<meta content="initial-scale=1.0, maximum-scale=1.0, user-scalable=no, width=device-width" name="viewport">
	<title>3445：[Usaco2014 Feb] Roadblock</title>
	<!-- css -->
	<link href="../css/base.min.css" rel="stylesheet">
	<link href="../css/project.min.css" rel="stylesheet">
	
	<!-- favicon -->
	<!-- ... -->
</head>
<body class="page-brand">
	<header class="header header-transparent header-waterfall ui-header">
		<ul class="nav nav-list pull-left">
			<li>
				<a data-toggle="menu" href="#menu">
					<span class="icon icon-lg">menu</span>
				</a>
			</li>
		</ul>
		<a class="header-logo header-affix-hide margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Usaco2014 Feb] Roadblock</a>
		<span class="header-logo header-affix margin-left-no margin-right-no" data-offset-top="213" data-spy="affix">[Usaco2014 Feb] Roadblock</span>
	</header>
	<nav aria-hidden="true" class="menu" id="menu" tabindex="-1">
		<div class="menu-scroll">
			<div class="menu-content">
				<a class="menu-logo" href="../index.html">BZOJ离线题库</a>
				<ul class="nav">
					<li>
						<a class="waves-attach" data-toggle="collapse" href="#problems">题目</a>
						<ul class="menu-collapse collapse in" id="problems">
							<li>
								<a class="waves-attach" href="../index.html">主页</a>
							</li>
							<li>
								<a class="waves-attach" href="../list.html">题目列表</a>
							</li>
						</ul>
					</li>
					<li>
						<a class="collapsed waves-attach" data-toggle="collapse" href="#about">关于</a>
						<ul class="menu-collapse collapse" id="about">
							<li>
								<a class="waves-attach" href="../about.html">关于此项目</a>
							</li>
						</ul>
					</li>
					
				</ul>
			</div>
		</div>
	</nav>
	<main class="content">
		<div class="content-header ui-content-header">
			<div class="container">
				<h1 class="content-heading">
                [Usaco2014 Feb] Roadblock                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
		</div>
		<div class="container">
			<section class="content-inner margin-top-no">
				<div class="row">
					<div class="col-lg-13 col-md-13">
						<div class="card margin-bottom-no">
							<div class="card-main">
								<div class="card-inner">
									
                                <h3>题目描述</h3><p><p><span style="font-family: 宋体;">有一个无向图，共</span><span lang="EN-US">N</span><span style="font-family: 宋体;">个节点，编号</span><span lang="EN-US">1</span><span style="font-family: 宋体;">至</span><span lang="EN-US">N</span><span style="font-family: 宋体;">，共</span><span lang="EN-US">M</span><span style="font-family: 宋体;">条边。</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">在节点</span><span lang="EN-US">1</span><span style="font-family: 宋体;">，它想到达节点</span><span lang="EN-US">N</span><span style="font-family: 宋体;">。</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">总是会选择最短路径到达节点</span><span lang="EN-US">N</span><span style="font-family: 宋体;">。作为捣蛋的奶牛</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">，它想尽量延迟</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">到达节点</span><span lang="EN-US">N</span><span style="font-family: 宋体;">的时间，于是</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">决定从</span><span lang="EN-US">M</span><span style="font-family: 宋体;">条边之中选择某一条边，使得改边的长度变成原来的两倍，由于智商的问题，</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">不知道选择加倍哪条边的长度才能使得</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">到达</span><span lang="EN-US">N</span><span style="font-family: 宋体;">号节点的时间最迟。注意：不管</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">选择加倍哪条边的长度，</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">总是会从</span><span lang="EN-US">1</span><span style="font-family: 宋体;">号节点开始走最短路径到达</span><span lang="EN-US">N</span><span style="font-family: 宋体;">号点。</span><span lang="EN-US">&nbsp;</span></p></p><hr/><h3>输入格式</h3><p><p><span lang="EN-US">&nbsp;</span><span style="font-family: 宋体;">第一行，两个整数</span><span lang="EN-US">N</span><span style="font-family: 宋体;">和</span><span lang="EN-US">M.&nbsp;1&nbsp;&lt;=N&lt;=250,&nbsp;1&lt;=M&lt;=250000</span><span style="font-family: 宋体;">。</span><span lang="EN-US">&nbsp;</span></p>
<p class="MsoNormal"><span lang="EN-US">&nbsp;</span><span style="font-family: 宋体;">接下来有</span><span lang="EN-US">M</span><span style="font-family: 宋体;">行，每行三个整数：</span><span lang="EN-US">A</span><span style="font-family: 宋体;">，</span><span lang="EN-US">B</span><span style="font-family: 宋体;">，</span><span lang="EN-US">L</span><span style="font-family: 宋体;">，表示节点</span><span lang="EN-US">A</span><span style="font-family: 宋体;">和节点</span><span lang="EN-US">B</span><span style="font-family: 宋体;">之间有一条长度为</span><span lang="EN-US">L</span><span style="font-family: 宋体;">的无向边。</span><span lang="EN-US">1&lt;=L&lt;=1000000</span><span style="font-family: 宋体;">。</span><span lang="EN-US">&nbsp;</span></p></p><hr/><h3>输出格式</h3><p><p><span lang="EN-US">&nbsp;&nbsp;</span><span style="font-family: 宋体;">一个整数。</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">选择了加倍某一条边的长度后，奶牛</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">从节点</span><span lang="EN-US">1</span><span style="font-family: 宋体;">到达节点</span><span lang="EN-US">N</span><span style="font-family: 宋体;">的最短路径是多少。但是输出的格式有变化，假设</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">没有加倍某一条边的长度之前，</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">从</span><span lang="EN-US">1</span><span style="font-family: 宋体;">号节点到达</span><span lang="EN-US">N</span><span style="font-family: 宋体;">号节点的最短路径是</span><span lang="EN-US">X</span><span style="font-family: 宋体;">；在</span><span lang="EN-US">Bessie</span><span style="font-family: 宋体;">加倍某一条边的长度之后，</span><span lang="EN-US">FJ</span><span style="font-family: 宋体;">从</span><span lang="EN-US">1</span><span style="font-family: 宋体;">号节点到达</span><span lang="EN-US">N</span><span style="font-family: 宋体;">号节点的最短路径是</span><span lang="EN-US">Y</span><span style="font-family: 宋体;">，那么你输出的结果是</span><span lang="EN-US">Y-X</span><span style="font-family: 宋体;">。</span><span lang="EN-US">&nbsp;</span></p></p><hr/><h3>样例输入</h3><pre>5 7
2 1 5
1 3 1
3 2 8
3 5 7
3 4 3
2 4 7
4 5 2
INPUT DETAILS: There are 5 fields and 7 pathways. Currently, the shortest path from the house (field 1) to the barn (field 5) is 1-3-4-5 of total length 1+3+2=6. </pre><hr/><h3>样例输出</h3><pre>2
（把节点3到节点4的边从原来的长度3变成长度6）   </pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Gold</p>
								</div>
							</div>
						</div>
					</div>
				</div>
				
				
			</section>
		</div>
	</main>

	<div class="fbtn-container">
		<div class="fbtn-inner">
			<a class="fbtn fbtn-lg fbtn-brand-accent waves-attach waves-circle waves-light waves-effect" data-toggle="dropdown" aria-expanded="true"><span class="fbtn-text fbtn-text-left">Menu</span><span class="fbtn-ori icon">apps</span><span class="fbtn-sub icon">close</span></a>
			<div class="fbtn-dropup">
				<a class="fbtn fbtn-brand waves-attach waves-circle waves-light waves-effect" href="../list.html" target="_self"><span class="fbtn-text fbtn-text-left">题目列表</span><span class="icon">menu</span></a>
				<a class="fbtn fbtn-green waves-attach waves-circle waves-effect" href="../index.html" target="_self"><span class="fbtn-text fbtn-text-left">返回主页</span><span class="icon">home</span></a>
				<a class="fbtn waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/submitpage.php?id=3445" target="_blank"><span class="fbtn-text fbtn-text-left">提交代码</span><span class="icon">send</span></a>
				<a class="fbtn fbtn-orange waves-attach waves-circle waves-effect" href="http://www.lydsy.com/JudgeOnline/wttl/wttl.php?pid=3445" target="_blank"><span class="fbtn-text fbtn-text-left">试题讨论</span><span class="icon">chat</span></a>
				
			</div>
		</div>
	</div>

	<!-- js -->
	<script src="../js/jquery.min.js"></script>
	<script src="../js/base.min.js"></script>
	<script src="../js/project.min.js"></script>
</body>
</html>